[M_a_t_t]

Another possibility is that it only leaks when the fuel pump is on. So you might not notice anything in the garage. Have you tried letting it idle and watching for leaks then? Does it smell like gas after you get out right after shutting it off?

I have also read (about my van's engine, it might be applicable to yours) that it is possible for gas to leak into the intake and use the extra gas there, but this usually comes with a poor running issue.

I think if it is running fine, then it must be leaking before the engine somewhere.

Just some suggestions,
Matt